Many electronic devices employ an electronic visual display. Touchscreen displays have become popular over the last decade, particularly in the context of mobile devices. Capacitive and resistive touch screen technologies have been widely deployed but have limitations, for example with respect to electrical properties of the touch input, optical clarity, and multi-touch capability.
Optical touchscreen are a promising technology that has many advantages. Optical touch screens may use FTIR (frustrated total internal reflection) where light (e.g., from an LED) is injected into a glass or acrylic glass substrate. Current state of the art LED packaging places an LED chip either at horizontal (0°) or vertical (90°) position within a package. Vertical placement requires additional space on the edge of the glass and interfacing of the package to the glass is difficult. Horizontal placement necessitates a light diffuser on top of the glass to scatter emitted light into shallow incident angles. A light diffuser is generally incompatible with “glass-to-edge” displays and results in low injection efficiency/higher optical power demands.
State of the art optical touch screen displays therefore currently require a 7 mm to 12 mm wide boarder around the edge of a display to implement optical touch technology. While this may not be an issue with larger displays, this is a significant barrier for smaller touch displays, for example of the type that may be employed in smart phones, tablets, and ultrabooks, etc., which benefit most from glass-to-edge displays, thin designs, low power, and low cost.
Miniaturization of optical touch screen technology generally entails integration of optical transceivers, integrated circuits, board & system design, and low-cost packaging heretofore unavailable.
Manufacturable methods, photonic device packaging architectures, and assemblies addressing the limitations of existing vertical and horizontal photonic chip packaging are therefore advantageous, and may prove a critical path in advanced optical touchscreen technology.